Process for the electrolytic production of tetramethyl lead



United States Patent 16 Claims. io1.204 s9 This invention relates to a process for the electrolytic production of tetramethyl lead.

A number of processes are known which permit the production of metal alkyl compounds, particularly tetraet-hyl lead and metal alkyls containing higher alkyl groups, by electrolysis with the use of, for example, lead anodes and preferably with the use of aluminum-organic complex compounds'serving as electrolytes. Examples of these processes include those disclosed in U.S. Patent 2,985,568, U.S. Patent 3,069,334, application Serial No. 262,285, filed February 4, 1963, U.S. Patent 3,164,538, application Serial No. 258,102, filed February 4, 1963, application Serial No. 320,607, filed October 29, 1963.

Among the reasons for the advance in the art achieved by these processes over the conventional production of, for example, tetraethyl lead from a sodium-lead alloy and ethyl chloride is the fact that, in the electrolytic process, the lead is completely dissolved at the anode to form lead alkyl While, in the conventional process, only about 25% of the lead contained in the sodium-lead alloy react in the manner desired. The remaining 75% must be worked up and recovered continually.

An electrolytic process which is specifically directed to the production of tetramethyl lead and which is attractive on a commercial scale has not as yet been described. One of the main difllculties encountered in carrying out such an electrolytic process on a commercial scale was the fact that suitable complex compounds containing methyl groups and usable as electrolyte baths in such an electrolytic process were not readily available up to the present. Aluminum alkyl complex compounds containing methyl groups have now become readily available by processes such as that disclosed in application Serial No. 193,330, filed May 8, 1963 and assigned to the assignee hereof (process for the production of sodium-organic complex compounds of aluminum and boron). These processes offer the possibility to proceed to the electrolytic production of tetramethyl lead on a commercial scale. The invention does not only take advantage of the fact that electrolyte complex compounds containing methyl groups can be produced by the process mentioned above but also provides a novel electrolytic process for the production of tetramethyl lead by combination with other essential features, this process constituting a technical progress.

It is an object of this invention to provide a process for the production of tetramethyl lead by electrolysis on lead anodes of complex compounds of elements of main group III of the Periodic Table, which complex compounds contain alkyl groups, the process comprising using electrolytes which contain aluminum complex compounds of the general formula MAl(CH (OR').,, wherein M is an alkali metal, particularly sodium and/ or potassium, R represents alkyl, cycloalkyl or aryl radicals or aryl radicals, preferred being alkyl radicals and cycloalkyl radicals in this order, and m is 1 to 4.

The production of tetramethyl lead by the new proce s of the invention is not simply analogous in every respect to the corresponding electrolytic production of metal alkyls containing higher alkyl groups. A number of problems different from those which, for example, are to be solved in case of tetraethyl lead are encountered in largescale performance of the electrolytic process carried outwith the use of complex compounds containing methyl groups as electrolyte.

In the above-mentioned electrolytic processes for the production of, for example, tetraethyl lead, fused baths of aluminum-containing organic complex compounds are used. The alkali metal-aluminum complexes containing 4 methyls and used in the process of the invention have a melting point which is sufliciently high that they cannot be used in an analogous manner for the production of tetramethyl lead in a continuous process operated for an extended period of time Where the electrolyte would have to exposed continually to the high temperature. Since other potential methyl complexes, e.g., those of the type MeAl(CH OR', undergo disproportionation in the melt at higher temperatures in accordance with the equation with precipitation of the very sparingly soluble and highmelting MeAl(CH the use of these compounds as fused electrolytes is also restricted.

It has now been found very surprisingly during the work done on the development of the new process that solutions of the electrolyte complex compounds in solvents can be used in place of the fused electrolytes invariably used up to the present. In this preferred embodiment of the invention, the electrolytic process is operated with electrolyte baths which consist of solutions containing aluminum complex compounds of the general formula MeAl(CH (OR') Examples of suitable solvents include inert polar solvents, particularly inert, polar organicsolvents such as tertiary amines or ethers, the latter being preferred. Aromatic hydrocarbons may also be used to a limited extent. Particularly preferred solvents are open-chain or cyclic ethers, particularly suitable being cyclic ethers, especially those of the te-trahydroifu'rane type. Other cyclic and straight-chain ethers such as d-iox-ane, diethyl ether, dibutyl ether; polyethers such as ethylene glycol-dialkyl ether and the like, may also be used in the process of the invention. It may be desirable to use relatively high-boiling solvents, particularly those having boiling points higher than that of tetramethyl lead.

Particularly suitable solvents are tetrahydrofurane or its homologues. Electrolyte solutions prepared with their exhibit surprising characteristics. If, for example, a solution of NaAl(OH in tetrahydrofurane is subjected to electrolysis, it is found that this solution has an approximately constant conductivity with a miximum of conductivity at medium concentrations. The conductivity drops greatly only with very dilute solutions. This situation is illustrated by the data in the following Table I.

TABLE I.CONDUCTIVITY OF SOLUTIONS OF NELA1(CH3)4 IN THE AT 60 C.

As may be seen, the most favorable range of concentrations for the electrolysis in the system described is between about 40 and about gms. of aluminum-organic complex compound per 100 ml. of tetrahydrofurane. Thus, it is possible in accordance with the invention to effect very extensive electrolytic dissociation of the electrolyte solution without having to put up with a substantial reduction in conductivity. The importance of this phenomenon, particularly with respect to the economy of the electrolytic process, is'obvious.

It is known that the conductivity of potassium-organic complex compounds is generally higher than that of sodium-organic complex compounds. Accordingly, it is possible in accordance with the invention and even preferred under certain circumstances to operate with the use of appropriate potassium complex compounds. In this case, it is possible, for example, to convert sodium-containing complex compounds into those of potassium by means of the processes of said 320,607 and Germant patent application Z 8,715. As is known, these processes involve thetreatment of sodium-containing complex compounds of aluminum and boron with potassium amalgam With exchange of the alkali metal between the complex and the amalgam. V

Accordingly, when starting, for example, from the complex compound KAl(CH the situation is as follows:

The solubility of the potassium compound is somewhat lower than that of the sodium compound in tetrahydrofurane. The amount of NaAl(CH dissolved in 100 ml. tetrahydrofurane is 67.2 gms. at 100 C. and 54.7 gms. at 66 C. In contrast, only about 40 gms. of the corresponding potassium-aluminum tetramethyl compound are dissolved in the same amount of solvent at 66 C. However, the conductivity of the dissolved potassium complex compound is higher than that of the dissolved sodium complex compound at the same concentration. Comparative-data are listed hereafter in Table II.

TABLE II Grns. MeA1(OH )4/100 ml. C. Conductivity 40 gms. KAl(CI-I )4 60 3.0 10- ohmscm. 40 gms. NaA1(CH )4 60 2.0X10- ohn1scm.-

ductivity (from 3.0 to 2.3 10 ohms" cmf will occur in spite of the wide difference in concentrations.

The use of solvents, particularly tertiary amines and ethers, has an additional essential advantage. It is known from former work of applicant, e.g., from US. Patent 3,164,538, that it may be particularly advantageous to use a mercury cathode in carrying out such electrolyses for the production of metal alkyl compounds. Among the advantages involved in the use of a mercury cathode is the fact that, when using sodium-aluminum-organic complex compounds as electrolytes, the anodically formed free aluminum trialkyl does not tend to re-decomposition with the cathodically formed sodium amalgam.- Thus, the electrolysis may be carried out without any risk without separation of the anode space from the cathode space. However, it has further been found that any liberated potassium in the form of potassium amalgam tends to enter into undesirable decomposition reactions with free aluminum trialkyl liberated at the anode. Therefore, operation with a pure potassium electrolyte, which would have been desirable for reasons of conductivity, has been impossible heretofore or required extraordinary precautionary measures.

If, in the process of the invention, solutions of these aluminum complex compounds are decomposed at a mercury cathode with formation of potassium amalgam at the cathode, then it is found that such undesirable reaction between anodic decomposition products and the amalgam liberated at the cathode does not longer occur. This is due to the fact that the solvent present, e.g., tetrahydrofurane, immediately combines with the free aluminum trimethyl liberated at the anode to form the corresponding tetral1ydrofuranate.' This addition product is substantially less reactive with potassium amalgam than is free aluminum trimethyl. Thus, it is also possible in accordance with the invention to operate with pure potassium-aluminum-organic complex compounds dissolved in a solvent, e.g., tetrahydrofurane, as electrolytes on a mercury cathode and, in doing so, to form potassium amalgams up to relatively high concentrations of, for example, 1% and more without having to comprehend undesirable redecompositions. This involves an additional facilitation of the process of the invention.

While the process of the invention and its advantages have been described above with reference to a specific aluminum complex compound of the general formula MAl(CH i.e., the-oxygen-free aluminum tetramethyl complex compound, it is within the scope of the invention touse mixtures of different electrolyte complex compounds in special embodiments of the process of the invention. However, all of these mixtures are characterized by the presence of at least one aluminum complex compound MAl(CH (OR') These aluminum complex compounds intervene actively in the reaction mechanism as essential constituents of the electrolyte in all of these special embodiments preferred in individual cases.

For example, when using an electrolyte which contains the aluminum complex compound MAl(CH then free aluminum trimethyl is formed as a dissociation product of the electrolyte in addition to tetramethyl lead. As is known, free aluminum trialkyls react with alkoxyaluminum complex compounds of the general formula MAIRgOR with reformation of the aluminum tetraalkyl complex compound and simultaneous formation of the free alkoxy aluminum dialkyl compound. Thus, it is possible with the use of a mixture of the aluminum tetramethyl complex compound and the alkoxy aluminum complex compound to suppress the formation of free aluminum trimethyl as long as aluminum alkoxy compleX compound is still present in the electrolyte mixture. At the same time, the dialkyl aluminum alkoxy compound is then isolated in free state in addition to tetramethyl lead. This procedure is applied in one embodiment of the process of the invention. This embodiment may entail several advantages. Thus, it is possible by variation of the alkoxy group to adjust the boiling point of the free alkoxy aluminum compound formed in addition to tetramethyl lead in a manner such as to permit easy separation of the two compounds by distillation. Also, regeneration may under certain circumstances be effected easier and with less troubles when proceeding via these dialkyl-aluminum alkoxy compounds than via aluminum trialkyls. This variation of the process of the invention may also be modified in a manner such that the electrolysis is effected with the altuninum tetramethyl complex compound alone while the reaction with the alkoxy-aluminum complex compounds in the sense described is carried out subsequently, e.g., outside the electrolytic cell.

While different aluminum complex compounds are combined in the embodiment described above of the process of the invention, it is also possible in other embodiments of the invention to use compounds containing other complexes and alkyl radicals in addition to the aluminum compound. In particular, mixtures of aluminum and boron complex compounds are used in these embodiments.

Thus, it is known that boron tetraalkyl complex compounds of the general formula MBR, can be used in the electrolytic production of metal alkyls. In one embodiment of the invention, the alkali metal-boron tetramethyl complex compound MB (CH is mixed with the.

aluminum complex compound MAl(CH (OR') used in accordance with the invention. Thus, for example, the aluminum complex compound MAl(CH OR' is used together with the alkali metal-boron tetramethyl compound in one embodiment. This also results in the formation of the product mixture of tetramethyl lead and free alkoxy-aluminum dimethyl already described for the case of aluminum complex mixtures. The boron complex compound remains unchanged and stationarily in the cell, i.e. it quasi acts only as a conducting salt while the aluminum alkoxy complex compound is decomposed and continually supplied to the cell. tablish particularly favorable conditions with respect to conductivity, it is even possible to operate in a manner such that a preponderant amount of boron complex compound is invariably and stationarily present in the cell while the oxygen-containing aluminum complex compound is supplied only at a rate which corresponds to the rate at which the free alkoxy-aluminum dimethyl is formed as the product of the electrolysis. In addition to, or in place of, the oxygen-containing aluminum complex compound MAl(CH OR', it is also possible in accordance with the invention to use the corresponding alkali metal-aluminum tetramethyl complex compound together with the boron tetramethyl complex compound. Here again, the aluminum compound actively intervenes in the course of the reaction.

A special embodiment of the invention combines known and novel characteristics into a novel process which permits the electrolytic production of tetramethyl lead with best results in spite of the presence of a solvent in the electrolyte and the concomitant difficulties encountered in separating tetra-methyl lead from the mixture of substances produced during electrolysis.

If the mercury cathode in accordance with U8. Patent 3,164,538 is used in this case, the following rules apply to the electrolysis stage:

Use is made of electrolytes which contain aluminum complex compounds wherein m reaches a value of at least 3, i.e., compounds where m is 3 and/or 4.

The preferred electrolyte is a liquid mixture containing up to 950 parts by weight of the electrolyte complex compound in 100 parts of tetrahydrofurane, particularly preferred being the above-mentioned relative proportions Where maximum conductivity is obtained. The electrolysis is then effected at a temperature in the range between about 50 and about 100 C.

The procedure used in recovering the tetramethyl lead and regenerating the electrolyte is determined by the nature of the electrolyte bath used.

Tetramethyl lead may be withdrawn from the electrolyte in a very simple manner by distillation, particularly by distillation in vacuo. This may be done either in the cell itself by using electrolysis in the vacuum cell as repeatedly described in earlier suggestions of applicant or after the electrolysis 'in a separate reaction step. In

case of low-boiling solvents, e.g. tetrahydrofurane, therewill first distil a mixture of tetrahydrofurane and tetramethyl lead which is easily separated in a column boiling point of tetrahydrofurane, 65 C., B.P. of tetramethyl lead, 110 C.). The tetrahydrofurane recovered by this distillation is then re-used for dissolving the distillation bottoms. The resultant solution of the exhausted electrolyte which is free from tetramethyl lead is passed to the regeneration unit. These distillations are performed successfully and particularly smoothly and safely if a hydrocarbon having about the same boiling point as tetramethyl lead is added to the mixture to be distilled. An example of a suitable hydrocarbon is isooctane. While tetramethyl lead is then obtained only in mixture with, for example, the same amount of this hydrocarbon, this mixture is just as suitable for use as antiknock compound as is pure tetramethyl lead itself.

The compounds separated from the reaction product and formed by dissociation of the electrolyte, e.g.,

To es- I Al(CH OR or Al(CH may be re-converted into the electrolyte complex compound with methyl halide, particularly with methyl chloride, and an alkali metal by the process described in application 193,330, filed May 8, 1962 (process for the production of alkali metal-organic complex compounds of aluminum and boron). This conversion may, if desired, be effected directly within the electrolyte mixed with sodium used, for example, in finely divided form. After filtration, the electrolyte may be returned into the electrolytic cell without further treatment. A

If the aluminum tetramethyl complex compound in tetrahydrofurane is exclusively used in the electrolysis, the addition compound aluminum trimethyl-tetrahydrofuranate is formed as was already mentioned. This compound is very stable and boils Without decomposition at 90 to 91 C./13 mm. Hg, i.e., about 80 to 90 C. above the boiling point of tetramethyl lead. Therefore, the separation of tetramethyl lead by distillation is accomplished without any difficulty.

The electrolyte is then regenerated by mixing it with sodium and introducing methyl chloride. In doing so, the tetrahydrofurane necessary to dissolve the electrolyte is liberated from its combination with aluminum trimethyl. The reaction is preferably effected at a temperature between 50 and 160 C. in accordance with the following equation:

The aluminum complex compound and tetrahydrofurane return into the electrolyte. In carrying out the regeneration described above, it may happen in case of insufiicient care used in performing the reaction that part of the material reacts in accordance with the equation:

This results in the formation of metallic aluminum which can be reconverted into the complex compound in a laborious manner only. I

If it is desired to avoid these difiiculties, it is possible when operating with aluminum-organic electrolytes to have recourse to the trick described above, i.e. operating in the presence of complex compounds of the formula Consistent with the amount of current passing through, this oxygen-containing complex compound is added in an amount just suflicient that the free aluminum trimethyl which is formed is immediately reconverted into the tetramethyl complex compound and the compound Al (CH 0R is formed. The regeneration, i.e., the reaction with methyl chloride in a sodium suspension then proceeds via this oxygen-containing aluminum compound which does not entail any difi'lcultly. When operating in this manner, it is particularly preferred to use oxygen-containing complex compounds in which the OR group contains a sufiiciently high number of carbon atoms, e.g., more than 3 and preferably from 6 to 10. This will shift the boiling point of the free alkoxy aluminum dimethyl compound in a manner such that easy separation from the tetramethyl lead by distillation becomes possible.

In the electrolysis, four atoms of alkali metal dissolved in mercury are obtained for every molecule of tetramethyl lead which is formed, this alkali metal being sodium amalgam in case of sodium-containing electrolytes and potassium amalgam in case of potassium-containing electrolytes. The potassium amalgam may also be converted into sodium amalgam by exchange with sodium containing electrolytes.

It is possible, particularly by means of the process of application 299,689, filed July 31, 1963, to recover metallic sodium from the sodium amalgam and to use this metallic sodium for the regeneration of the electrolyte.

This reduces the overall expenditure of metallic sodium in the process of the invention to that which corresponds to the equation:

Since the lead is completely converted into tetramethyl lead although, as will be shown hereafter, somewhat more than the calculated amount of lead goes into solution, and the consumption of alkali metal is limited to the minimum amount necessary, the process of the invention is distinguished by an extremely high economy.

Example 1 The electrolytic apparatus used for the experiments described hereafter comprised a cylindrical glass vessel having a surface-ground upper edge and a capacity of 1 liter. The vessel was sealed on top with a plane cover of an insulating plastic material (Bakelite). The cover was provided with openings for inserting a thermometer and the lead-in wire for the cathode, a screwed-in socket with ground joint for mounting a reflux condenser, a nozzle for passing over a protective gas and the stirrer bearing for the rotary lead anode. The bottom of the glass vessel contained a mercury pool of 300 ml. Provided above the mercury surface at a distance of about l mm. was the lead anode which was a circular lead disc of 15 mm. thickness and 6 cm. diameter suspended horizontally. This disc simultaneously served as the stirrer for the electrolyte and, therefore, was equipped at its border with a plurality of inclined blades. The lead disc was screwed into a vertical hollow shaft. Inserted into the bore of this shaft was a glass stirrer which stirred the mercury at a speed of rpm. while the lead anode rotated at a high speed. A solution of 200 gms. N-aAl(CH in 400 gms. of tetrahydrofur-ane was introduced into this cell under a protective gas atmosphere and the electrolysis was effected for 7 hours at 90 C. and a terminal voltage of 5.5 v. with 3.8 amperes, i.e.,14 a./dm. Thereafter, the reaction solution was removed from the electrolytic cell by siphoning and tetrahydrofur-ane and tetramethyl lead formed were distilled off into a cooled receiver while gradually raising the temperature of the oil bath from 70 to 90 C. and finally applying a vacuum of 20 to 30 mm. Hg. Then, after having changed the receiver, aluminum trimethyltetrahydrofuranate was distilled off at 90 to 91 C. and 13 mm. Hg. The distillation residue consisted of NaA1(CH3)4 and could be reused for another electrolysis after dissolution in tetrahydrofurane which had been separated from the tetramethyl lead by distillation with a 50 cm. Vigreux column. The residue obtained after having distilled off the tetrahydrofurane is substantially pure tetramethyl lead which may be subjected to another purification by steam distillation.

The yield of tetramethyl lead was 60 gms. (90% of the amount calculated from the amount of current) and the reduction in weight of the anode was 57 gms. 12% more than corresponds to the calculated amount), i.e., small amounts of lead are dissolved as lower-grade lead methyls which, however, then disproportionate to form lead and tetramethyl lead. (The electrolyte turns black during electrolysis and then contains suspended lead powder which, however, can be separated easily during the work-up procedure.) The yield of aluminum trimethyltetrahydrofuranate is 144 gms. (100% of the theoretical). The sodium amalgam was 0.56%, which corresponds to 23 gms. Na (-=100% of the theoretical amount).

Similar results are obtained when repeating the experiment described above with the following solvents: Diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, d-ioxane, 1,4-butanediol-dimethyl ether, 1,4butanediol-diethyl ether, triethylamine, et-c.

8 Example 2 A solution of 200 gms. NaAl(CI-I in 400 ml. of tetrahydrofurane is subjected to electrolysis underthe conditions and in the apparatus described in Example 1. A solution of 224 gms.

Na(CHa) BAlO o 112- H-O Hn in 200 ml. tetrahydrofurane is allowed to How in continuously within 7 hours from a stock vessel at a rate which is consistent with the amount of current passing through. After 26.8 a-hr. have passed through, the electrolysis is discontinued. The react-ion solution is removedby siphoning and a mixture of tetrahydrofurane and tetramethyl lead is distilled oil as described in Example 1. Then the residue from distillation is heated to about to C. (measured in the liquid) under a vacuum of 10- mm. Hg. In doing so, 186 gms.

i.e., 100% of the theoretical amount, distil. The alkoxyaluminum dimethyl may be reconverted with sodium in finely divided form and methyl chloride into by the process of Serial No. 193,330, filed May 8, 1962 (process for the production of sodium-organic complex compounds of aluminum and boron) and re-used for another electrolysis. The residue from distillation is pure NaAl(CH which is dissolved in 400 gms. of recovered tetrahydrofurane and used as electrolyte for another electrolysis.

Example 3 A solution of 220 gms. NaAl(CH in 400 guns. of tetrahydrofurane was electrolyzed for about 14 hours at 100 C. and 3.8 a. (i.e. about 15 a./dm. in the apparatus described in Example 1. A terminal voltage of about 5 v. was necessary to maintain the current density mentioned above. A solution of 190 gms. NaB(CH in 145 gms. of tetrahydrofurane was allowed to drop into the electrolytic cell at a rate consistent with the amount of current passing through, i.e., 25 gms./hr. A receiver cooled to 80 C. was provided downstream of the reflux condenser. In this receiver, the boron trimethyl which formed was condensed. Upon termination of the electrolysis, tetrahydrofurane and tetramethyl lead were distilled off commonly from the electrolytic cell and separated by fractionation as described in Example 1.

The distillation residue is NaAl(CH which is dissolved in part of the tetrahydrofurane recovered and may thus be re-used for another electrolysis.

Yield of tetramethyl lead 126 gms. (94%). Yield of boron trimethyl 106 gms. (95% Yield of sodium in form of sodium amalgam 46 gms.

Similar results are obtained when substituting the following solvents for. tetrahydrofurane in the experiment described above: Di-n-propyl ether, di-isopropyl ether, din-butyl ether, di-sec. butyl ether, ethyl-n-butyl ether, ethylhexyl ether, methyl-octyl ether, methyl-decyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, dioxane, 1,4-butanediol dimethyl ether, 1,4-butanediol diethyl ether, tetrahydro-furfural glycol :acetal, tetrahydro furfural-l,3-propanediol acetal, ologimers of tetrahydrofurane of the type R-[O-(CH -OR wherein It may be 2, 3 and 4; tertiary amines such as triethylamine, tributylamine, methylethylpropylamine, dimethyl anilin, diethyl aniline, tetramethyl-hexamethylene diamine.

Example 4 The procedure is the same as in Example 1 except that a solution of 200 gms. NaAl(CH in 500 gms. diglyme is used as the electrolyte. Electrolysis is effected at 100 C. and 7.6 a., i.e. 30 a./dm. the terminal voltage necessary to maintain the current density being about 8 v. The electrolysis is discontinued after about 2.5 to 3 hours, the appropriate moment being perceptible by an increase in terminal voltage. The reaction solution is removed from the electrolytic vessel by siphoning and the tetramethyl lead formed by electrolysis is distilled off under a vacuum of about 50 mm. Hg while gradually raising the bath temperature to 85 C. and while cooling the receiver to -80% C.

1 96% of the theoretical.

Example 5 The procedure is the same as that decribed in Example 4 except that triglyme mixed with by volume of toluene is used as the solvent under otherwise identical conditions.

Example 6 A solution of 250 gms. NaA1(CH (-On butyl) in 400 gms. of tetrahydrofurane is electrolyzed' for 7 hours at 3.8 a. and about 9 v. in the apparatus decribed in Example 1. Upon termination of the electrolysis, the reaction solution was removed from the electrolytic vessel by siphoning and tetrahydrofurane and tetramethyl lead produced are distilled off while gradually increasing the temperature of the oil bath from 70 C. to 90 C. and finally applying a vacuum of 20-30 mm. Hg. The mixture of tetrahydrofurane and tetramethyl lead was subsequently separated by distillation with a 50 cm. Vigreux column. The distillation residue of the first distillation was heated to 120 C. under a vacuum of 5 mm. Hg. In doing so, 127 gms. Al(CH OC I-I (B.P., 80 C./5 mm. Hg) distilled oil. The residue was pure NaA1(CH OC H The yield of tetramethyl lead was 63 gms., Le. 94% of the theroetical. Moreover, 127 gms.,

(98% of the theoretical amount) were obtained. The sodium amalgam was 0.56%, which corresponds to 23 gms. Na (100% of the theoretical amount).

Example 7 The electrolysis may be effected with the use of the corresponding potassium complex compounds using the same procedure as described in Examples 1 to 6.

What is claimed is:

1. A process for the production of tetramethyl lead by electrolysis on lead anodes of complex compounds of elements of main group III of the Periodic Table, which complex compounds contain alkyl groups, which comprises using electrolytes which contain an aluminum complex compound of the general formula wherein M is selected from the group consisting of sodium, potassium and mixtures of sodium and potassium, R is selected from the group consisting of alkyl, cycloalkyl, and aryl, and m is 1-4.

2. The process of claim 1, wherein said electrolyte bath is a solution of said aluminum complex compound in an inert organic solvent.

3. The process of claim 2, wherein said solvent is selected from the group consisting of aromatic hydrocarbon, inert polar solvent, straight-chain and cyclic ether, and mixtures of these compounds.

4. The process of claim 2, wherein said electrolysis is elfected at temperatures of from about 50 to about C.

5. The process of claim 1, wherein mixtures of different aluminum complex compounds of the formula a)m( ')4 m are used.

6. The process of claim 5, wherein said mixture is a mixture of MA1(CH and MAl(CH OR'.

7. The process of claim 1, wherein an alkali-boron tetramethyl complex compound is added to said electrolytes containing said aluminum complex compound of the general formula MA1(CH (OR) 8. The process of claim 7, wherein the aluminum complex compound MA1(CH OR is used together with said alkali meta1-boron tetramethyl.

9. The process of claim 7, wherein the aluminum complex compound MA1(CH is used together with said alkali metal-boron tetramethyl compound.

10. The process of claim 1, wherein use is made of an electrolyte which is a liquid mixture of from 5 to 950 parts by weight of said organometallic complex compound in 100 parts by weight of tetrahydrofurane.

11. The process of claim 1, wherein said electrolytes are mixtures consisting of diflerent organometallic complex compounds and contain oxygen-containing complex compounds of the formula MA1(CH OR' as one component and said oxygen-containing aluminum complex compounds are added to the electrolyte at a rate at which they are consumed in the electrolysis with formation of the compound Al(CH OR.

12. The process of claim 11, wherein tetramethyl lead is produced with the use of an oxygen-containing aluminum complex compound wherein the OR group contains more than 3 carbon atoms and preferably from 6 to 10 carbon atoms.

13. The process of claim 1, wherein use is made of an aluminum complex compound wherein m is at least 3.

14. The process of claim 1, wherein the tetramethyl lead is recovered from the elecrolyte by distillation.

15. The process of claim 1, wherein the exhausted residual electrolyte freed from tetramethyl lead is mixed with finely divided sodium and then treated with methyl halide and free methyl compound selected from the group consisting of boron and aluminum methyl compounds and is thereby regenerated with formation of the starting complex compounds.

16. The process of claim 1, wherein only the compound MA1(CH is electrolyzed and the resultant reaction product is reacted with the compound MA1(CH OR'.

References Cited by the Examiner UNITED STATES PATENTS 2,849,349 8/1958 Ziegler et al. 204-59 2,944,948 7/ 1960 Giraitis 204-59 3,028,320 4/1962 Kobetz et a1. 20459 3,028,323 4/1962 Kobetz et a1. 20459 3,088,885 5/1963 McKay 20459 3,164,538 1/1965 Ziegler et a1. 204-59 JOHN H. MACK, Primary Examiner.

JOHN R. SPECK, Examiner. 

1. A PROCESS FOR THE PRODUCTION OF TETRAMETHYL LEAD BY ELECTROLYSIS ON LEAD ANODES OF COMPLEX COMPOUNDS OF ELEMENTS OF MAIN GROUP II OF THE PERIODIC TABLE, WHICH COMPLEX COMPOUNDS CONTAIN ALKYL GROUPS, WHICH COMPRISES USING ELECTROLYTES WHICH CONTAIN AN ALUMINUM COMPLEX COMPOUND OF THE GENERAL FORMULA 